There has been a long felt need for a simple, inexpensive and accurate device for dispensing a predetermined amount of fluid directly from a reservoir of that fluid without the need for separate measuring devices such as cups and/or measuring spoons. This need has existed, with varying requirements as to accuracy and service conditions, in such widely varying applications as dispensing of cough syrups, liquid soaps, detergents, antacids, traditional and veterinary medications, as well as the accurate dispensing of fluid components for various formula in research and development laboratories and hospitals.
A particularly advantageous application of such a device would be in the dispensing of both ethical and over-the-counter liquid medications. Although the dispensing of such medications does not, in many cases, require an analytical degree of accuracy and reproducibility, the usual approach of "teaspoon measurement" leaves much to be desired. For example, due to the many varied designs and capacities of teaspoons, a "one teaspoon" measurement could vary from 4 to 7.5 ml. In addition, an appreciable error can be introduced in the measuring process by the individual making the measurement; for example, an individual may habitually undercut the measurement to avoid spillage, whereas another individual may actually take a "heaping teaspoonful" in order to ensure good measure. It follows that, as the number of teaspoons required for the desired dosage increases, this margin of error is compounded. With regard to tablespoon measurement an even wider variance is encountered, and the actual quantity of medication administered could be anywhere from 12 to 24 ml. depending on the particular spoon used and the individual measuring the dosage. Also, when the particular medication is to be mixed with water or other liquid, the separate measuring device not only represents a possible source of inaccurate measurement but also a serious source of possible bacterial or viral contamination.
Another use for such a device would be in measuring and administering medication to individuals suffering from handicaps, neuromuscular disorders or debilitating diseases such as, for example, multiple sclerosis, Parkinson's disease, blindness or other condition where dispensing and/or administering the liquid medication utilizing a spoon or cup would be difficult or impossible. Currently, when the individual for whom medication is prescribed is, for instance, blind or has poor eyesight he must rely on supervisory personnel to dispense an accurate dosage. In the alternative, he can use a "braille" cup having raised annular rings formed in the sidewalls thereof to indicate the various dosages. Measurement using this device is accomplished by placing a finger within the cup at the appropriate ring representing the correct dosage and pouring the medication into the cup until the fluid level reaches the finger. The drawbacks of these methods are readily apparent. Full or part-time supervisory personnel are becoming increasingly expensive and the "braille" cup method is prone to potentially life-threatening inaccuracies.
In the field of veterinary medicine, there has also been a long felt need for measuring and dispensing apparatus capable of accurately and efficiently administering fluid medication to animals. To date this procedure has been accomplished through the use of tubes and eyedroppers wherein the veterinarian or owner would draw the correct dosage into the eyedropper or tube, insert the spout into the animal's mouth and expel the fluid. This method generates problems in that, should the animal fail to swallow the medication, a second application would be required. Further, repeated contact between the animal's mouth and the eyedropper, and then the eyedropper and the reservoir of medication, results in potentially dangerous contamination to the medication remaining in the reservoir.
Many devices have been proposed for the dispensing of controlled-volume increments of fluids from containers, but all have suffered from one or more of a number of disadvantages. For example, many of the proposed devices which operate by means of pressurizing the container holding the fluid have been prone to inaccuracy and erratic operation brought about by pressure differences between the ambient atmosphere and the vapor space over the fluid inside the device. Designs of this type tend to create a partial vacuum inside the container caused either by fluctuations in the ambient temperature and pressure or by altitude differences between the point where the dispenser is first joined to the container and the point of use. The partial vacuum could also be created by repeated withdrawals of fluid from the device without replacing the volume thus lost with an equivalent volume of air. This pressure differential tends to impede the flow of fluid out of the dispenser, resulting in dispensing of inaccurate dosages. By the same logic, an excess pressure in the apparatus will tend to promote an undesirably large outflow of the fluid causing an overdose or spillage.
This difficulty does not arise when the container is opened to the atmosphere to dispense a measured dosage with each use. However, when the container itself is opened directly to the atmosphere there is the attendant danger of spillage and/or contamination.
Devices which do not require opening for each use generally effect pressure equalization by allowing air to bubble into the reservoir of liquid medication simultaneously with the withdrawal of liquid therefrom. Heretofore this method required that the dispenser construction be rather complex to allow for the measured dispensing of the liquid and simultaneous pressure equalization. Some of these devices even made use of differential air pressure to control the flow of liquid and thereby cut off the flow at a desired volume. Such devices, however, require sophisticated and expensive mechanical construction.
While the foregoing description of the background of the invention has been directed primarily in terms of measuring and dispensing of medication, it will be recognized that the same considerations apply, with varying degrees of emphasis, to a wide variety of other applications.